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You never hand over a password. Every connection goes through Meta's own authorisation screen, and you can revoke it from there at any time, independently of us.
Meta's own platform rules (not ours) generally require an Instagram account to be a professional account linked to a Facebook Page before its DMs can be managed through the official API, and a WhatsApp number to be registered on the WhatsApp Business Platform. If something is missing, the connect screen will say so rather than fail silently.